1. Field of the Invention
The invention relates to devices for indicating the number of fluid dispensations remaining in a container from which metered dispensations are made.
2. Brief Description of Related Art
A wide variety of fluid dispensers are known and commercially available to dispense metered proportions of a contained fluid from containers. For example, U.S. Pat. No. 3,749,290 describes a trigger actuated dispensing pump assembled with a fluid container. Upon actuation, a measured proportion of the contained fluid is dispensed from the containers.
Of particular importance as fluid dispensers are metered dose inhalers (MDI) employed to administer fluid medications to animals, including humans.
The use of inhalers is well known and the art has developed over the past twenty five years to cover many versions of the basic concept of a "pumping" type medication applicator. The device may be manually pumped (such as described in U.S. Pat. No. 5,284,132) or a pumping like cycle may be utilized. The medication may also be repeatedly released from a pressurized disposable canister to create repeated sprays or inhalations as needed.
Representative of the early inhalers for oral and intra-nasal administration of medications are those described in, for example, U.S. Pat. Nos. 3,361,306; 3,183,907; 3,565,070; 4,206,758; 4,803,978; 4,934,358; 4,955,371; 5,060,643; and 5,351,683. Representative of nasal-pharyngeal inhalers for large mammals such as a horse is that described in U.S. Pat. No. 5,062,423.
Metered dose inhalers (MDIs) are, at present, the most efficient and best-accepted means for accurately delivering medications in small doses to an animal's respiratory tract. Therapeutic agents commonly delivered by the inhalation route include bronchodilators (B.sub.2 agonists and anticholinergics), corticosteroids, and anti-allergics. Inhalation may also be a viable route for anti-infective, vaccinating, systemically acting and diagnostic agents, as well as anti-leukotrienes, anti-proteases and the like.
MDIs are available in several types. Most frequently, MDIs comprise a pressure resistant container (canister) typically filled under super-atmospheric pressures with a product such as a drug dissolved in a liquified propellant, or micronized particles suspended in a liquified propellant. The container is fitted with a metering valve. The valve is movable from an inner (charging) position to an outer (discharging) position. A spring bias holds the valve in the charged position until forced to the discharge position. Actuation of the metering valve allows a metered portion of the canister content to be released, whereby the pressure of the liquified propellant carries the dissolved or micronized drug particles out of the container and to the patient. A valve actuator also functions to direct the aerosol as a spray into the patient's oropharynx. Surfactants are usually dissolved in the aerosol formulation and can serve the dual functions of lubricating the valve and reducing aggregation of micronized particles.
Representative of pharmaceutical formulations for use in metered dose inhalers are those described in U.S. Pat. No. 5,190,029. The MDI devices for administering such pharmaceutical formulations are also well known as seen for example in the descriptions given in U.S. Pat. Nos. 3,361,306; 3,565,070; and 4,955,371 which are incorporated herein by reference thereto.
A disadvantage arising from use of the known devices is that the patient cannot determine the amount of medicament in the aerosol container at any given time. The containers are generally not transparent to view, being light protective of the contents. Shaking them will not always reveal auditory information as to their contents. In an extreme case this could mean that the patient, possibly suffering from severe bronchospasm or like emergency condition and needing a dose of medicament, will find that the aerosol container will not dispense a dose, because its contents have been previously exhausted. The problem has been recognized and consideration given to solutions. For example, U.S. Pat. No. 4,817,822 describes an inhaler device which includes a counting means for indicating the relative emptiness of a container or the number of doses dispensed. However, this inhaler counting mechanism is physically attached to the aerosol container as well as the inhaler, such as by a retaining ring or retaining cap. In one embodiment, the counting means is a separate sleeve fitting on the up-turned bottom of the aerosol container. It is easy to lose, not being integrated with the inhaler, but an ancillary unit slipped over the loose aerosol container. In another embodiment, the counting means requires a secured attachment to the aerosol container neck, which prevents removal of the container from the inhaler, even when empty. The inhaler device is only useful for use with the original aerosol container and can not be used with aerosol refill containers.
The U.S. Pat. No. 5,020,527 presents an improvement over the dose counting means of U.S. Pat. No. 4,817,822 wherein the mechanical counter can be replaced with an electronic counter. The improved inhaler can indicate the number of doses remaining in the aerosol container. However, the device is not fool-proof in operation, which can be a disadvantage in the hands of a severely debilitated, confused or forgetful patient. In households which include small children they have been known to "play" with the MDI's when unsupervised access is possible. Infants can accidentally reset or interfere with established counts in the mechanical devices. For example, the counter can be accidentally reset, obviating its usefulness and, in fact, misleading of the patient as to the true number of doses remaining in the container. Also, the counter can not be automatically reset when a full, new aerosol container (refill) is to be used. This can affect the accuracy of the count carried out.
In addition, the inhaler of the U.S. Pat. No. 5,020,527 still employs a mechanical trigger to actuate the counting means. It is subject to triggering of the counter without actual administration of a dose from the container, for example, when the aerosol container is removed and the inhaler device washed and disinfected, independent of the aerosol container.
These, and other problems associated with the inhalers and other fluid dispensers of the prior art are solved by the present invention, described hereinafter. The device of the invention is economical to manufacture, assemble with fluid containers and disposable when the container is empty, in the same manner currently followed in disposing of the containers.
The device of the invention is intended for use with one fluid container and is disposable with it when the contents are emptied. One need not reset a counter with the errors attendant with such a procedure.